ZigBee Technology

For Innovative Technologies, ZigBee modules were an intelligent choice. Searching online, Innovative Technologies found a number of vendors offering 802.15.4/ZigBee modules. Two module characteristics were of key importance: power consumption and size. The sensor device has to work autonomously for 4 years on one 9V battery. Plus, the PCB board had very little "real estate" left for module integration. Most of the leading ZigBee modules boast very low power consumption. However, when it comes to size, only the ZigBit modules from MeshNetics featuring a tiny footprint of just over three square centimeters -met Innovative Technologies' requirements. The fact that ZigBit modules come bundled with the MeshNetics' own ZigBee networking stack software, along with support for both hardware and software, further boosted Innovative Technologies' confidence in their choice.

ZigBee-Based Wireless Sensor Network

The next step was to try out the ZigBit modules. Innovative Technologies ordered the ZigBee Evaluation Kit from MeshNetics to achieve this goal. Containing three ZigBit-based development boards with sensors, accessories and software, the kit provided sufficient tools to evaluate the module's performance, ensuring that it lived up to expectations. After a successful test run, Innovative Technologies began prototyping their application.

ZigBit modules featuring dual chip antennas are integrated into boards connected with a range finder sensor and 9V battery. ZigBit modules take full advantage of the new Atmel's RF transceiver AT86RF230, which possesses -101dBm of Rx sensitivity and up to +3dBm of Tx power. This combination is known as the "link budget." Range of operation is a logarithmic function of link budget, so a difference of only 9 dBm nearly triples the range. Thanks to the outperforming link budget, the range of AT86RF230 is almost 3 times that of any other 2.4GHz 802.15.4 radio on the market today. This is important in a spacious parking lot. If a module provides a good range, it means that one sensor device can be used to cover several spaces. Besides, the parking lot environment, with its concrete walls, pillars and metal cars, is not exactly an RF signal-friendly place--making strong RF performance a must for the modules.